Portable battery



1.1 is a perspective view of a portable battery, showing my new design;

1.2 is a rear view thereof;

1.3 is a side view thereof;

1.4 is a top view thereof;

1.5 is a front view thereof; and

1.6 is a side view thereof.

In the drawings, the broken lines are for the purpose of illustrating environment only and form no part of the claimed design. 

CLAIM The ornamental design for a portable battery, as shown and described. 